Thermally stable high-strength porous alumina
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A two-step heating schedule involving pulse electric current sintering, a kind of pressure-assisted vacuum sintering, and a subsequent postsintering in air was used to fabricate sintered porous alumina compacts. During pressure-assisted vacuum sintering, a dense microstructure of the Al2O3–C system was obtained and in the second stage (i.e., during postsintering in air at different temperatures ranging from 800 to 1300 °C for more than 10 h) carbon particles present in the Al2O3–C system burned out to form a highly porous Al2O3 compact. In this work, the porosity (30%) was successfully controlled and did not change with the postsintering temperature. The intriguing aspect of this study is that porous alumina compacts are fabricated with high strength and remain stable against the postsintering temperature and extended soaking time. This behavior merits the material fabricated here as a potential porous compact, mechanically withstanding for high-temperature applications.
Recently, much interest has been shown in catalytic combustion at high temperatures for gas turbines, boilers, and jet engines, and, therefore, synthesis of catalyst supports stable at high temperatures has become important.1–3 In general, commercial catalysts are biphasic, being composed of a support material and one or more active phase component(s). The support provides a porous framework with a pore-size distribution permitting access to active sites for the reactants and free exit for the products. Therefore, designing the shape of the macropores and/or their modelization is an important field of research for catalyst and catalyst support developers. Materials with high meso- and microporosity and, in turn, high surface area also play an important role in developing catalyst supports. Likewise, another important property of a porous support is its mechanical strength. In large industrial reactors, the collapse of the structure (catalyst bed) under its own weight should obviously be avoided because it will result in a severe and not easily corrected pressure drop. Mechanical strength is also required when the catalytic system is subjected to vibrations (car exhaust systems, for instance) or to a very high gas or liquid flow velocity. Although many fabrication methods have been reported to improve the mechanical strength of porous supports,4–6 there is a lack of reports on the thermal stability of the mechanical properties of porous alumina compacts. Hence, the main interest of this paper is to fabricate a porous alumina support with high strength that can also be thermally stable. a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 4, Apr 2003
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Previously, we reported a fabrication method for highstrength and high-porosity alumina by pulse electric current sintering (PECS).6 The fabrication method involves composite processing (addition of 3 vol% 3Y·ZrO2) and doping (200 ppm MgO and 200 ppm TiO2). In this work, porous alumina compacts
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